An oscillating water column power generating apparatus (OWC) is designed for use in converting a waver energy into an air energy, and then for converting, by an air turbine, this air energy into a rotational energy of a turbine shaft.
Generally speaking, in the OWC, a box-type member consisting of a boundary side walls and a crown deck is installed at sea in such a condition that the foot of the boundary side walls is in normal soak in sea water; the crown deck of the box-type member is formed an air vent to form a guide path for guiding the air passing through the air vent. Disposed in the guide path is the air turbine. A generator is couped to the output shaft of the air turbine for driving thereof.
In the OWC, with the rise of a free water surface in a chamber formed in the box-type member, air in the chamber is pushed upward, there occurs an air stream flowing towards the guide path from the inside of the chamber; reversely with the descent of the free water surface In the chamber, there takes place an air stream in the guide path, flowing towards the chamber from the guide path. That is, the wave energy is turned into the air energy. The air turbine is turned by the air stream flowing through inside the guide path, converting the air energy of the air stream into the rotational energy of the air turbine output shaft. When a generator is driven by the output shaft of the air turbine, the rotational energy of the air turbine is converted into the: electric energy.
In the above-described OWC, the direction of the air stream flowing in the guide path is reversed alternately. In this case, it should be noted that the modulus of energy conversion will lower if the output shaft of the air turbine is not rotated in the same direction at all times by the air stream reversed alternatively in the direction of its flow.
A Wales turbine is known as this type of air turbine whose output shaft is kept on constantly rotating in one direction albeit the alternate reversion of the direction of flow of the air stream. In this Wales turbine, the central axis of the cylindrical wall inside surface is an axis of rotation, on which a rotary member of a spindle shape tapered at its both ends in the axial direction is supported freely rotatably within the guide path having the cylindrical wall inside surface, and also having a symmetrical blade section known as for example NACA0021 in the maximum diameter section of the rotary member; four turbine rotor blades are provided protrusively in a radial direction, in increment of 90 degrees of angle, with the chord line of the symmetrical blade section arranged in normal plane on the rotational axis.
The turbine rotor blades having the symmetrical blade section are designed to have an attack angle proportional to the speed of the air stream at a roundish leading edge section of the symmetrical blade section. Therefore, there takes place a lift force on the turbine rotor blades, the tangential component of the lift force rotates the rotary member of spindle shape. Since the turbine rotor blades have the chord line of the symmetrical blade section within a normal plane with rotational axis even when the direction of the air stream in the guide path is reversed, the direction of the rotational of the rotary member of spindle shape will not change.
In the Wales turbine, the maximum thickness part in the section of the turbine rotor blades is present in a position close to the leading edge of the blade; when a symmetrical blade section having a great blade thickness ratio (a ratio of the maximum blade thickness to a chord length), the turbine rotor blades can start of itself. In this case, however, the tangential component of the lift force arising on the turbine rotor blades decreases at a relatively low fluid speed, and at the same time a drag component increases, resulting in the ceiling revolution of the turbine and in a poor energy conversion modulus. On the other hand, with the maximum thickness part shifted to the trailing edge side and with the symmetrical blade section of a decreased maximum thickness ratio used, a high speed revolution of the turbine can be obtained at a high fluid speed, and a high modulus of energy conversion is obtained. In this case, a deteriorated starting property occurs, resulting in a failure in achieving self-starting at a low fluid speed.